1. Field of the Invention
The present invention relates to a heat-insulating agent for molten metal, which is used to cover a molten metal surface to thereby prevent the molten metal from being cooled or oxidized.
2. Description of the Prior Art
As a heat-insulating agent for molten metal, so far organic materials such as grain stems, grain seed husks, saw dust, etc., carbonaceous materials obtained by carbonizing these organic materials, and refractory materials such as vermiculite, diatomaceous earth, expanded perlite, alumina, silica sand, aluminum ash, etc., alone or in combination, have been used. Also, a heat-insulating and exothermic agent containing both an easily oxidizable metal powder such as aluminum or magnesium and an oxidizing agent such as iron oxide or a nitrate such as potassium nitrate, sodium nitrate, barium nitrate, etc., in combination, with the above described material has been used.
However, these heat-insulating agents have the following disadvantages.
With the above-described organic materials and the carbonized materials thereof, the time during which these materials are heat-insulating is short because these materials are easily burned by the heat of the molten metal and substantially disappear. Therefore, a large volume of these materials is required to heat-insulate for a long period of time. In addition, it is very difficult to handle or use these materials due to their low bulk density.
With the above-described refractory materials, the heat-insulating effect is insufficient and heat-insulating is particularly poor where the material is melted by the heat of molten metal.
Also, the above-described heat-insulating and exothermic agent provides satisfactory results for an extremely short period of time. However, this combination is not suitable for heat-insulating for the period of time ordinarily employed, because the heat-insulating property of the residue formed by the exothermic reaction is poor.